The invention relates to a process and an apparatus for reducing, dispersing, wetting and mixing pumpable, nonmagnetic multiphase mixtures by means of electromagnetic energy, which acts on magnetic working media within substances in a closed volume, the working media moving differently under the influence of an electromagnetic field, changing in location and/or over time.
In the case of processing materials by reducing--in particular by fine and ultrafine reduction of granular substances--and/or by mixing, dispersing and/or agitating powders, liquids and gases, at the forefront is the fact that as large a contact surface or surface of the interacting phases as possible has to be generated, since this shortens the duration of processing and reduces the temperature gradient and concentration gradient in the processing volume.
As is known, various technical designs of agitator ball mills are used for the process-engineering steps such as reducing, (deagglomerating), dispersing, wetting and mixing of pumpable, non-magnetic multiphase mixtures.
In the case of this preparation technique, the energy used is transferred to the multiphase mixtures only indirectly via a plurality of intermediate stages, beginning with the electric drive, via a rotating agitator and one or more grinding media. This results in high energy losses, which have to be led away as thermal losses via complex cooling systems.
Furthermore, on the material-discharge side of the working space, additional separating means, such as screens, edge filters etc., and shaft sealing systems are necessary, which are subjected to high material wear.
Also known are apparatuses and processes for mechanically preparing granular substances and/or for mixing and agitating powders, liquids and gases by the use of electromagnetic fields. Here, the electric energy fed to a stationary main element by means of electromagnetic fields is converted directly into mechanical energy of freely moving ferromagnetic working media. The stationary main element is, for example, an electrical exciter arrangement, which bears an exciter winding, and which has an air-gap space.
German Offenlegungsschrift 2,556,935 discloses a material working process for powders, liquids, gases and their mixtures as well as an apparatus for carrying out the process, in which the material to be worked is introduced into a chamber together with magnetic elements of hard-magnetic material, which move chaotically under the influence of an electromagnetic alternating field. The alternating field is generated by means of an electric exciter winding in a space in which the chamber is arranged. In this arrangement, the exciter winding surrounds the chamber. The magnetic elements are arranged in the chamber in a layer of predetermined thickness, the thickness being determined by the operating conditions of the magnetic field, the size of the magnetic elements, their density and their magnetic variables such as induction and coercive force as well as by the force of gravity.
In other material working processes, such as are described in U.S. Pat. Nos. 3,219,318, and 3,423,880, hard-magnetic ferromagnetic elements and magnetic alternating fields, in particular pulsating magnetic fields, are used.
In the case of these processes, first of all the material to be worked, of any form, is introduced into a chamber, and thereafter the ferromagnetic elements of a hard-magnetic material. Then, the chamber is put into a space in which a magnetic alternating field is generated. The magnetic field sets the ferromagnetic elements into a chaotic motion, in which they rotate about their axes and collide with one another, whereby the material is correspondingly worked.
In the processes according to the patents mentioned, the magnetic elements are produced from a hard-magnetic material with a coercive force of over 50 Oersted and have a non-spherical shape. Their average size lies in the range of at least a few tenths of a micrometer to at most 2.5 cm. The magnetic field strength of the alternating field is over 0.01 Oersted and its frequency is up to 1 MHz.
These processes serve for working substances in a periodic and uninterrupted operating sequence in small vessels, boxes, tubes or capillaries as well as for grinding surface locations where access is difficult.
The apparatuses with which said working processes are implemented include an electric solenoid winding and a working chamber of a non-magnetic material, arranged in the inner or outer space of the solenoid coil, in which a sinusoidal magnetic alternating field is generated. The magnetic elements introduced into the chamber, which are of barium hexaferrite or an "Alnico-8" alloy or iron-cobalt-nickel-aluminum alloy, of indeterminate form, effect by their motions under the influence of the magnetic field a mixing or reducing of the material being worked. The number of magnetic elements in the chamber is chosen such that they are at sufficiently great distances from one another during their motions in the chamber and do not wear one another down, this number being smaller than the number of elements in the case of their single-layer arrangement on the entire bottom surface of the chamber.
A disadvantage of the known processes is the low energy density which is introduced into the processing operations, due to the relatively small number of magnetic elements per unit volume of the working chamber. Consequently, great energy requirements arise, since there is not utilization of the entire volume of the magnetic field, per unit of the worked product, which causes the working of the material to be more expensive. It is found that an increase in the number of magnetic elements in the working chamber on the one hand results in great wear of the elements, whereby the product being worked is contaminated and the costs of the working increase on account of the high consumption of the expensive magnetic media, and on the other hand the lower-lying magnetic elements move less intensively than the upper elements, as a consequence of the force of gravity of the upper elements acting on the lower-lying elements.
In the known working apparatuses, an air-gap space is available as working space. In it there is a multiplicity of ferromagnetic working media, which act in the conventional sense as grinding media, and the substances or multiphase mixtures to be prepared.
For the exciter systems, in general three different types are used:
(1) Concentric alternating field exciter systems with single-phase fed ring or solenoid windings as are described, for example, in the following printed publications: Soviet Patent 480,447, German Offenlegungsschrift 2,556,935, Soviet Patent 662,144, Soviet Patent 837,411, Soviet Patent 908,389, German Offenlegungsschrift 3,843,368 U.S. Pat. No. 4,995,732; PA1 (2) Linear single-sided and two-sided travelling-field exciter systems with multiphase fed phase windings according to, for example, the following printed publications: Soviet Patent 995,221, Soviet Examined Patent Application 1,023,573, German Offenlegungsschrift 3,233,926, U.S. Pat. No. 4,601,431, German Offenlegungsschrift 3,240,021, U.S. Pat. No. 4,632,318, German Offenlegungsschrift 3,240,057, U.S. Pat. No. 4,632,316, Soviet Examined Patent Application 1,103,887; and PA1 (3) Rotationally symmetrical single-sided and two-sided rotating-field exciter systems such as are known from, for example, the following printed publications: German Patent 888,641, British Patent 1,570,934, Soviet Patent 808,146, Soviet Examined Patent Application 1,045,927, German Offenlegungsschrift 3,233,926, U.S. Pat. No. 4,601,431, and East German Patent 240,674. PA1 B--amplitude PA1 f--frequency of the exciter current PA1 t--time PA1 (1) the working space must be filled virtually completely with working media, PA1 (2) certain classifications (size and/or shape) of the working media must be maintained, and PA1 (3) there must be graduation in the radial field strength distribution. PA1 .tau..sub.p --Pole pitch of the exciter arrangement PA1 f--Frequency of the exciter currents PA1 (1) opposed connection of the exciter fields of the mutually opposite exciter systems over the entire length of the exciter system (Soviet Patent 995,221, German Offenlegungsschrift 3,233,926) or over certain sections (Soviet Examined Patent Application 1,023,573, Soviet Examined Patent Application 1,103,897); PA1 (2) changing the distance between mutually opposite exciter systems over their length (German Offenlegungsschrift 3,233,926, Soviet Examined Patent Application 1,103,897); PA1 (3) making the fields less uniform by various pole pitches, different feeding and dimensioning of the exciter windings of the mutually opposite exciter systems (German Offenlegungsschrift 3,233,926); PA1 (4) fitting partition walls in the working space transversely to the direction of movement of the exciter field (German Offenlegungsschrift 3,233,926).
In the case of alternating field exciter systems with single-phase fed ring or solenoid windings, the space enclosed by the winding is fully available as a working space for working the material. Ferromagnetic components are not required for guidance of the exciter field.
However, on the other hand there is first of all the necessary extra winding material used to ensure adequate working space field strengths and problems in leading away the current heat losses from the compact ring coils. The low heat transfer to the surroundings and the limited heat absorption capacity of the stream of material which apply in this case always require additional measures for adequate loss removal which, on the one hand, ensures that the magnetic characteristic values of the working media are not substantially reduced and, on the other hand, ensures that the material to be prepared does not heat up to above specified limit temperatures.
Furthermore, the exciter field B (x, t) in this case represents a pure alternating field EQU B (x,t)=B.multidot.cos (2.pi..multidot.f.multidot.t) (1)
where:
That means that at each location x of the working space only field changes of equal magnitude, that is changes over time, take place. They can also only bring about the same oscillatory or rotational motions of the working media.
To ensure the relative motions between the working media absolutely necessary for the mechanical loading of the substances to be prepared,
High degrees of filling with working media on the one hand limit significant dimensions of the preparation apparatus and consequently the material throughput, since the force of gravity and adhesion forces of the working media fix their maximum filling height (German Offenlegungsschrift 2,556,935). Beyond the critical filling height of the working media, inadequate working media motions are achieved, in particular in the lower regions. This results in a reduction in the energy input into the working space and in a reduction in the effectiveness of the working.
On the other hand, the high degrees of filling with working media bring about considerable wearing of the working media due to the frequent collisions of the working media.
In the case of alternating field exciter systems, it is functionally only possible for the required local field strength gradients to run radially inward. The field strength decreases exponentially over the inner extent of the exciter system. As a result, the motion of the working media, and consequently the effectiveness of the working, becomes less and less in the radially inward direction. Consequently, areas of dead space are possible in batch operation and it is possible for material to pass straight through in the case of continuous filling.
Designs with ring windings and solenoid windings are restricted to small diameter/length ratios and have low energy densities and low levels of efficiency.
The known linear travelling field exciter systems have a three-phase winding distributed in slots. For guidance and for ensuring penetration of the working space by the exciter field, a closed magnetic circuit of laminated sheet assemblies is required. The exciter field changes not only over time but also in location. The following applies for the fundamental wave: ##EQU1## where: B--Amplitude
That is to say, in the working space there is a sinusoidal induction distribution, which moves at a constant rate EQU v.sub.o =2.tau..sub.p .multidot.f
This natural field movement brings about a transportation of the ferromagnetic content of the working space. Consequently, the working media shift within a short time to one of the two ends of the working chamber, build up there and hinder one another in their motion. As a result, the possible energy conversion and level of efficiency are markedly reduced. Distinctly poorer and less uniform preparing effects are obtained. To counteract this disadvantage, in principle two opposite travelling field exciter systems are used and additional measures are taken to make the motion of the working media less uniform:
Although each of these measures brings about a reduction in the rate of transportation, it also brings about a significant reduction in the electromechanical energy conversion and consequently a deterioration in the level of efficiency. On the other hand, it involves considerable extra constructional and mechanical-engineering expenditure as well as increased expenditure on operational management and control as well as process-engineering handling.
In the case of rotating field exciter systems, in principle there are endless paths in the plane of the direction of movement of the field for the working media, since these exciter systems are self-contained.
In British Patent 1,570,934, an outer rotationally symmetrical rotating field exciter system and, for making the working media motion additionally less uniform, multiply polarized working media are used.
In the case of the known apparatus for reducing, mixing and agitating with opposite rotationally symmetrical rotating field exciter systems according to German Offenlegungsschrift 3,233,926, the disadvantage of this apparatus is that the directions of movement of the exciter fields of the outer system and of the inner system are opposed, and additional steps have to be taken for making the fields less uniform by variable pole pitches, magnetomotive forces and air-gap widths.
The constant, on average over time, translatory transporting movement is necessary in order to guarantee a steady-state electromechanical energy conversion in the working space of use for mechanical preparation. Therefore, as known from East German Patent 240,674--for intensive utilization of the electric energy supplied and for ensuring adequately great energy densities in the working space, it is only appropriate to design the exciter arrangement as opposite on two sides and self-contained, to design the working chamber as similarly self-contained and to make the dimensioning, connection and feeding of the exciter winding such that there is only a single direction of movement of the electromagnetic field penetrating the working chamber. This then produces endless paths for all the ferromagnetic constituents of the working chamber content, an effective energy conversion and corresponding preparation effects.
However, the self-containedness is accomplished in the direction of movement of the exciter field by an arrangement in series, provided with spaced intervals, of a plurality of geometrically finite exciter system parts.
Such an arrangement is suitable for the dry fine and ultrafine reduction of granular materials, but not for the mechanical preparation of pumpable multiphase mixtures.